Studying a group of bus drivers, for whom daily pleasantries can be part of the job, scientists found that those who engaged in "surface acting," or smiles and chipper voices, when they were actually have a bad day were more withdrawn from work. And the result seemed to be worse for women, which one professor suggested may relate to societal expectations of women as being more expressive.

On the other hand, those who created smiles by thinking positive thoughts, or engaged in "deep acting," seemed to actually cheer up, and their work output increased. Without a subscription to the Academy of Management Journal, it's hard to say how productivity was measured in a bus drivers' role, but it's suggested that fake smiles kept them apart from the task at hand.